The proposed research will evaluate the immune capabilities of three mosquitoes, Aedes aegypti (black-eyed Liverpool strain), Aedes aegypti (Rockefeller strain), and Aedes trivittatus. Specific information will be gained on the immune response of these mosquitoes against three species of filarial worms, Brugia pahangi, Brugia malayi, and Dirofilaria immitis. Experiments are designed to compare the volume of hemolymph, physical characteristics of hemolymph, total hemocyte numbers, and relative numbers of different types of hemocytes in these mosquitoes. Relative changes in the above values as a result of filarial worm infection also will be assessed. From these data a possible explanation for the difference in the immune capabilities of these mosquitoes will be sought. Additional studies will determine if the presence or lack of a sheath in B. pahangi microfilariae stimulates or prevents an immune response by mosquitoes. Experiments also are designed to determine if B. pahangi produces a substance that inhibits the immune response in general in Ae. aegypti, and if this inhibition can be transferred to another mosquito. Transmission electron microscopy studies will assess the ultrastructural characteristics of the encapsulation-melanization response of these mosquitoes against both sheathed and unsheathed microfilariae. The overall aim of this project is to clarify the role the immune mechanism plays in mosquito-filarial worm relationships, thereby increasing our understanding of the epidemiology of mosquito-borne filariasis.